North Korea would probably use nuclear weapons only if it perceived a threat to its survival, but the US remains uncertain how Pyongyang would define such a threat, the US intelligence chief said yesterday.

"Although we assess with low confidence that the North would only attempt to use nuclear weapons against US forces or allies to preserve the Kim (Jong-un) regime, we do not know what would constitute, from the North's perspective, crossing that threshold," James Clapper, director of national intelligence, said in an annual report to Congress on global security threats.

Although we assess with low confidence that the North would only attempt to use nuclear weapons against US forces or allies to preserve the Kim (Jong-un) regime, we do not know what would constitute, from the North's perspective, crossing that threshold

But the US faces a challenge trying to discern North Korea's strategic calculations when it comes to its nuclear weapons. "We do not know Pyongyang's nuclear doctrine or employment concepts," the report said.

The report said North Korea has exported ballistic missiles and associated materials to countries including Iran and Syria. It also displayed what appeared to be a road-mobile intercontinental ballistic missile and put a satellite in orbit with a launch vehicle.

"These programmes demonstrate North Korea's commitment to develop long-range missile technology that could pose a direct threat to the United States, and its efforts to produce and market ballistic missiles raise broader regional and global security concerns," the report said.

Clapper testified with new CIA Director John Brennan and FBI Director Robert Mueller. North Korea leader Kim Jong-un has threatened to "wipe out" a South Korean island amid fresh international pressure and new sanctions over the North's nuclear weapons and missile tests.

In assessing Iran, the report stated flatly that Tehran is developing nuclear capabilities to enhance its security and influence and "give it the ability to develop a nuclear weapon".

The report also said the core of al-Qaeda has been weakened.

"Al-Qaeda has suffered steady losses among its senior ranks since 2008, diminishing the network's central leadership to a point that the group is probably unable to carry out complex, large-scale attacks in the West," Clapper said in the report.

Additional reporting by Associated Press

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